The present invention relates to a multiple projection television system.
A multiple projection television system has been proposed to provide a large display.
FIG. 16 shows a conventional multiple projection television system. A plurality of projection units 1 are disposed in matrix to form a large display. As shown in FIG. 17, each projection unit 1 comprises a cubic casing 11 made of aluminum, a screen 6 secured to an opening member 2 provided in front of the casing 11, and a projector, such as a projector 20 shown in FIG. 19, provided in the casing 11 at a rear portion thereof. The projector comprises a trio of CRT projection tubes providing RGB images directed to the screen 6. The projector is mounted in the casing 11 at the rear.
The screen 6 comprises a Fresnel lens 4 and a lenticular sheet 5. The screen 6 is attached to the opening 2 of the casing 11 with four support frames 10 and screws 9.
FIG. 18 shows a bordering frame 18 between adjacent screens, which acts as a mounting structure of the screen 6 to the casing 11. The bordering frame 18 comprises opening members 2, a pair of stoppers 3 and support frames 10. The stopper 3 is secured to an inner peripheral portion of each of four sides of the opening member 2. The outer periphery of the screen 6 is mounted on the stopper 3. The support frame 10 is mounted on the screen 6 corresponding to the stopper 3, and secured to walls of the opening member 2 with screws 9. Thus, the screen 6 is secured to the casing 11, interposed between the stoppers 3 and support frames 10.
When the screen 6 is to be removed from the casing 11, all of the screws 9 and the support frames 10 are removed from the casing.
In such a structure, external parts such as screws and frames are needed, thereby increasing the weight of the casing 11. Accordingly, it is inconvenient to carry the projection unit 1. Furthermore, it is difficult to maintain the projection unit in a setting state.
FIG. 19 shows another conventional projection unit comprising a plurality of frames, thereby solving the above mentioned disadvantages. A projection unit 13 comprises a cabinet 14 comprising a plurality of frame members 15. The screen 6 is secured to a front portion of the cabinet 14. A base plate 16 for the projector 20 is provided between lower frame members 15 at a rear portion of the cabinet.
As shown in FIG. 20, a plurality of cabinets 14 are mounted in matrix. Thereafter, the projector 20 is inserted in each cabinet 14 from the rear and mounted on the base plate 16 as shown in FIG. 21.
In the projection unit, it is necessary to provide a predetermined distance between the screen 6 and the projector 20 for obtaining a proper optical path length. Therefore, the projector 20 is disposed at the rear portion, and it is preferable to insert the projector at the rear.
If there is no space behind the jointed cabinets 14, since the screen 6 can be removed from the cabinet 14 by removing screws 9 and support frames 10, the projector 20 is inserted at the front of the cabinet. In such a mounting operation, it is necessary to carry the projector 20 in the cabinet 14 to the base plate 16 at the rear portion. The projector 20 is usually at 30 to 60 kg in weight, and the optical path length is about 700 mm from the screen 6. Therefore, it is essentially impossible the mount the projector in the cabinet 14 at the front. Furthermore, the projector 20 may damage the frame members 15 each of which has a thin thickness.
In the multiple projection television system, it is important to reduce the width of the bordering frame 18 between the screens. However, in the above mentioned system, the width of the bordering frame is determined by the widths of the adjacent support frames 10. As a result the width of the bordering frame can not be reduced.
Since four sides of the screen 6 are supported by support frames 10 and screws 9, the number of screws 9 is large.
It is necessary to remove all of the support frames 10 for removing the screen 6, causing the number of steps of the process to increase.